Systems and Methods for Downhole Communications Using Power Cycling

ABSTRACT

Systems and methods for using power cycle events to cause a downhole tool to change its operational state and/or transmit a data stream to the downhole tool. In one embodiment, a tool such as a gauge for an ESP is positioned downhole in a well and is configured to receive power from a control unit at the surface of the well. The control unit power cycles the downhole tool to communicate a need to modify the operational state of the tool. The tool may include a non-volatile memory to store an indicator of the tool&#39;s current operational state. When the tool is power cycled, the operational state is modified and the indicator is updated. The power cycling may cause the tool to increment through available operational states, or the timing of the power cycles may convey parameters or other operating information to the downhole tool.

BACKGROUND

1. Field of the Invention

The invention relates generally to communications in well systems, and more particularly to systems and methods for using power cycle events to cause a downhole tool to change its operational state.

2. Related Art

The efficient operation of wells to produce oil and gas or other fluids involves the collection and processing of large amounts of data. This data is commonly collected by tools such as gauges that are positioned downhole in the wells. These gauges are typically designed to continually sense downhole conditions and transmit data corresponding to the sensed conditions to control equipment positioned at the surface of the well.

Downhole tools may communicate their data to surface equipment in several ways. For instance, the downhole tools may be coupled to the surface equipment via dedicated communication lines, or they may be configured to communicate data over a power cable. Because of the expense of providing a dedicated data line, communication over a power cable (“comms-on” communications) has become a viable and common alternative.

Most comms-on systems are designed to enable the transmission of data from downhole to the surface, rather than from the surface to the downhole tools. It is extremely difficult to implement two-way communications in comms-on systems. Those comms-on systems that enable two-way communications are generally only able to achieve this through the implementation of complex frequency modulation schemes and/or other complex signal varying methods that require the use of expensive modulation components or a significant addition of electronic hardware downhole.

It would therefore be desirable to provide simpler, more cost effective means to enable communication of data such as control and configuration information from surface equipment to downhole tools using only the existing system hardware and comms-on architecture.

SUMMARY OF THE INVENTION

Embodiments of the present invention may reduce or eliminate the foregoing problems by providing a means for downhole communication that does not require additional receiver or transceiver hardware as needed in conventional systems for receiving communications from surface equipment. The present systems and methods instead use power cycle events to communicate a need to change the operational state of the downhole tool and/or send limited amounts of data.

One embodiment comprises a system installed in a well, where the system includes control equipment, a downhole tool and a power cable coupled between the control equipment and the downhole tool. The control equipment is positioned at the surface of the well. The downhole tool is positioned within the wellbore of the well. The control equipment is configured to control the delivery of power through the power cable to the downhole tool and to thereby selectively power cycle the downhole tool. The downhole tool is configured to modify its operation in response to power cycle events or sequencing.

Another embodiment comprises a downhole tool such as a gauge for an electric submersible pump (ESP), where the tool is configured to modify its operation in response to power cycle events or sequencing. In one embodiment, the downhole tool includes non-volatile memory which is configured to store an indicator of the current operational state of the downhole tool. When the tool is power cycled and the operational state is modified, the indicator is updated to reflect the changed state. The non-volatile memory may store state information, operating parameters, lookup tables or other information relating to the operation of the tool. In one embodiment, the downhole tool is configured to increment its operational state each time it is power cycled. In another embodiment, the tool is configured to determine the timing of a series of power cycle events (e.g., delays between the events), and to modify its operation based on the timing of the power cycle events. The timing information may be interpreted by the downhole tool indicating a desired state, a parameter value, or other operating information. The communication scheme can be extended in a binomial or monomial fashion thereby providing an improved data compression technique.

Another embodiment comprises a method implemented in a downhole tool such as a gauge package. The method includes powering up the tool and thereby causing the tool to operate in a first operational state, and power cycling the tool to cause it to operate in a second operational state which is different from the first operational state. The operational state may be changed by incrementing through several available states, where the state is incremented once each time the downhole tool is power cycled. Alternatively, the operational state may be changed by determining the timing of a series of power cycle events, interpreting the timing to identify a corresponding state change, and implementing the identified change. The various state changes may involve changing the function of the downhole tool, or the parameters that are used in the operation of the tool.

Another embodiment comprises a downhole gauge tool for an ESP, where the tool not only accepts power cycle sequencing as a means of mode selection, but also accepts power cycle sequences to update various data parameters within the gauge's memory and/or communicates a formalized data packet structure. First, a mode could be activated via a power cycle sequence to initiate the acceptance of following power cycle transmissions as pieces of a data stream. Data compression methods can be implemented via a custom binary based protocol to enhance data throughput. One data compression technique, for example utilizes binary states in addition to varying bit widths. A high binary state is signified by “power on” whereas a low state is determined by the absence of power. Bit widths can, for instance, be implemented via the elapsed time during the “power on” state. Both the binary state and different bit widths can be orchestrated in a compressed manner to enhance data throughput as opposed to only using a binary incremental counter method. For example, if a series of four power cycles is implemented, and the on-states are sequentially transmitted with three on-time thresholds, then a base-4 interpretation could yield a base-2 compression ratio of 50% (4 power cycle events/8 bits). By varying both the number of power cycle events and the number of defined time thresholds per event, better compression ratios can be realized. This would greatly enhance the capability of sending more complex data, as opposed to a simplistic counter based method previously discussed.

Numerous other embodiments are also possible.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention may become apparent upon reading the following detailed description and upon reference to the accompanying drawings.

FIG. 1 is a diagram illustrating an exemplary system for communicating to a downhole tool in accordance with one embodiment.

FIG. 2 is a functional block diagram illustrating the structure of a downhole tool in accordance with one embodiment

FIG. 3 is a timing diagram illustrating the modification of the operating state of a downhole tool in response to power cycle events in accordance with one embodiment.

FIG. 4 is a state diagram illustrating the modification of the operating state of a downhole tool in accordance with one embodiment.

FIG. 5 is a flow diagram illustrating a method in accordance with one embodiment.

FIGS. 6A and 6B are timing diagrams illustrating the timing of sequences of power cycle events in accordance with one embodiment.

FIG. 7 is a state diagram illustrating possible state changes corresponding to detected timing of power cycle events in accordance with one embodiment.

While the invention is subject to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and the accompanying detailed description. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular embodiment which is described. This disclosure is instead intended to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

One or more embodiments of the invention are described below. It should be noted that these and any other embodiments described below are exemplary and are intended to be illustrative of the invention rather than limiting.

Generally speaking, the present systems and methods provide means for communicating information from surface equipment to a downhole tool used in wellbore operations, where power cycle events caused by the surface equipment are used to cause the downhole tool to modify its operation.

One embodiment is implemented in a system installed in a well to produce oil, gas or other fluids. The system includes a downhole tool such as a gauge package, surface equipment that provides power to the downhole tool, and a power line coupled between the downhole tool and the surface equipment. The downhole tool includes a transmitter which is configured to transmit data to the surface equipment. The data may be transmitted over the power line in a comms-on system, or it may be transmitted over a separate data line.

In either case, the downhole tool does not have a conventional receiver (or transceiver) that is capable of receiving and demodulating data from the surface equipment. The downhole tool is instead configured to detect power cycle events and to modify its operation based on the detected events. In one embodiment, the downhole tool begins operating in an initial state when powered up, then increments to a different operating state upon being power cycled. Alternatively, the downhole tool may be configured to determine the timing between a plurality of power cycle events and to change its operating state according to the timing of the events. The modification of the operating state may involve a change of functionality, a change of operating parameters, or both.

Referring to FIG. 1, a diagram illustrating an exemplary system in accordance with one embodiment of the present invention is shown. In this embodiment, an ESP system is implemented in a well for producing oil, gas or other fluids. An ESP 120 is coupled to the end of tubing string 150, and the ESP and tubing string are lowered into the wellbore to position the ESP in a producing portion of the well (as indicated by the dashed lines at the bottom of the wellbore). Surface equipment that includes a drive system 110 is positioned at the surface of the well. Drive system 110 is coupled to pump 120 by power cable 112, which runs down the wellbore along tubing string 150. Tubing string 150 and power cable 112 may range from less than one thousand feet in a shallow well, to many thousands of feet in a deeper well.

ESP 120 includes a gauge package 123 which is attached to the bottom of a motor section 121 of the ESP. ESP 120 may include various other components which will not be described in detail here because they are well known in the art and are not important to a discussion of the invention. Motor section 121 is operated to drive the ESP thereby pumping the oil or other fluid through the tubing string and out of the well. Gauge package 123 senses operating conditions (e.g., temperature, pressure, flow rate, etc.) in the wellbore. Drive system 110 produces power that is suitable to drive motor section 121, as well as to power gauge package 123. This output power is provided to motor section 121 via power cable 112.

Drive system 110 includes a control unit 113 that controls the power provided to gauge package 123. Control unit 113 can power up, power down, or interrupt and resume power to gauge package 123 (i.e., power cycle the gauge package). The manner in which control unit 113 power cycles gauge package 123 can cause the gauge package to change its operating state, potentially changing the functionality of the gauge package, or changing the operating parameters used by the gauge package. Control unit 113 may power cycle gauge package 123 in response to, for instance, user input, control information received from other surface equipment, or feedback information provided by the gauge package itself.

Referring to FIG. 2, a functional block diagram illustrating the structure of a downhole tool in accordance with one embodiment is shown. In this figure, a downhole tool 200 such as a gauge package is coupled to a power line 210. Power line 210 is connected to a power regulation and transmitter unit 220. Power regulation and transmitter unit 220 regulates (e.g., filters) the power received via line 210 and provides power to the reminder of the components in the tool.

As depicted in the figure, downhole tool 200 includes a sensor 260 which is configured to monitor conditions such as temperature or pressure in the wellbore, temperature of the ESP motor, flow rate, or the like. The output of sensor 260 is received by signal acquisition and processing unit 250, which may filter or otherwise process the signals. Signal acquisition and processing unit 250 outputs sensor data to central processor 230, which manages the operation of the downhole tool. Central processor 230 provides the sensor data to power regulation and transmitter unit 220, which communicates the data to the surface equipment via power line 210.

It should be noted that, while FIG. 2 depicts a comms-on system in which data is transmitted to the surface via the power line (210), alternative embodiments of the invention need not be comms-on systems. The data could instead be transmitted on a communication line that is separate from the power line. This separate line may be a separate conductor which is contained with the power line in a single cable, or it may be an entirely separate cable.

In the embodiment of FIG. 2, central processor 230 is configured to detect power cycle events. Central processor 230 interprets the power cycle events and timing, and modifies the operation of downhole tool 200 as needed. A clock 270 may be provided to allow the timing of power cycle events to be determined. Although the timing of power cycle events is preferably performed while the apparatus is powered on, a battery, capacitor bank or other energy storage device may be included in the system to provide sufficient power to enable real time clocks or other components of the downhole tool to function through power cycles.

Non-volatile memory 240 is coupled to central processor 230 and provides means to store information relevant to the modified operation of the tool. For instance, non-volatile memory 240 may store state information corresponding to different operation states of the tool, operating parameters for the different states, firmware for implementing the functionality of various operating states, and so on.

It should be understood that the functions of the various illustrative functional blocks, units, subsystems and the like which are described in connection with this and other embodiments are intended to be exemplary, rather than limiting. The functionality described herein may be implemented in more or fewer components, it may be allocated to different components than those shown here, or it may otherwise vary from the specific examples provided in this disclosure.

Referring to FIG. 3, a timing diagram illustrating the modification of the operating state of a downhole tool in response to power cycle events in accordance with one embodiment is shown. The line voltage (Vline) provided to the downhole tool is depicted at the top of the figure as a function of time. The state of the downhole tool is shown below the line voltage. When an operating voltage is applied to the power line at time t₁, the downhole tool is powered up and begins operating in an initial state. This may, for example, be the normal operating state of the tool. In the case of a gauge package, the device may begin sensing conditions and transmitting corresponding data to the surface equipment.

At some point, it may be desirable to change the operating state of the downhole tool. The tool is then power cycled by dropping the line voltage to zero at time t₂ and then reapplying the operating voltage at time t3. The duration of the voltage interruption may vary, depending upon the design of the tool and the desired effect of the power cycle. In this embodiment, the interruption is relatively brief and provides an indication to the downhole tool that the operating state of the tool should be modified. As shown in the figure, upon detecting the power cycle, the downhole tool switches from the initial operating state to a second operating state. In this second state, the downhole tool may implement different functions in the initial state. For example, the second state may be used to cause the tool to perform diagnostic functions or to modify the configuration of the tool. In one embodiment, the downhole tool continues to operate in the second state until the tool is power cycled again. In alternative embodiments, the tool may be configured to revert back to the initial state or switch to another state after a predetermined period, or after completion of a defined set of tasks. Other variations are also possible.

Referring to FIG. 4, a state diagram illustrating the modification of the operating state of a downhole tool in accordance with one embodiment is shown. Four different states are illustrated in this figure—an initial state (S1), and three additional states (S2-S3). In this embodiment, the downhole tool is configured to increment through the different states in which it may operate. When the downhole tool is powered up, it operates in initial state S1. Upon the occurrence of a power cycle, the downhole tool transitions from the initial state to state S2. Upon the occurrence of the next power cycle, the tool transitions from state S2 to state S3. Successive power cycle events cause the downhole tool to switch from state S3 to state S4, from state S4 to the initial state, from the initial state to state S2, and so on. The downhole tool may implement this behavior by maintaining an indicator of the current state in a non-volatile memory. Whenever a power cycle event is detected, the indicator is advanced to the next state. The tool then operates in accordance with the indicated state.

Referring to FIG. 5, a flow diagram illustrating a method in accordance with one embodiment is shown. In this method, power is provided to the downhole tool (500), which causes the tool to initiate a startup routine (510). As part of the startup routine, the downhole tool checks a counter in a non-volatile memory (520). The counter may have been initialized with a value corresponding to a normal operational state. The downhole tool then increments the counter (530). If the tool is not power cycled (540), the tool proceeds to complete the startup routine and operation in the state first indicated by the counter. If the downhole tool is power cycled (540), the tool returns to the top of the procedure and begins the startup routine again (510). When the counter is checked again (520), the counter will have been incremented, so the tool will proceed in the newly indicated state. The counter will be incremented again (530) in case the tool is power cycled again (540). If the tool is not power cycled, the tool will proceed to operate in the indicated state (550).

In the embodiment of FIGS. 3 and 4, power cycle events are used to communicate to the downhole tool only the need to switch states. In an alternative embodiment, additional information can be provided to the downhole tool through the timing of the power cycle events. For instance, the downhole tool can be configured to interpret intervals during which the tool is powered on between successive power cycle events. Referring to FIGS. 6A and 6B, timing diagrams illustrating the timing of a sequence of power cycle events in accordance with one embodiment are shown. FIG. 7 is a state diagram illustrating possible state changes corresponding to detected timing of power cycle events.

FIGS. 6A and 6B show two examples of the timing of successive power cycle events. In the first example (shown in FIG. 6A), a first power cycle event is detected by the downhole tool. At time t₁, the tool is powered on. At a time t₂, the downhole tool is powered down. The interval between t₁ and t₂ is d₁. In the second example (shown in FIG. 6B), a first power cycle event occurs, with the downhole tool being powered on at time t₃. At a time t₄, a second power cycle event occurs, so the tool was powered on for an interval of d₂. In each case, the downhole tool determines the interval during which the tool was powered on and interprets the meaning of the delay. This might be done, for example, by finding the interval and the corresponding meaning in a lookup table. The tool can then act in accordance with this meaning.

In one embodiment, the delay may correspond to a particular desired state. Referring to FIG. 7, a group of possible states S₀-S_(n) are shown. The transition from state S₀ to each of states S₁-S_(n) is associated with a corresponding delay. For instance, the transition from state S₀ to state S₁ is associated with the delay d₁, the transition from state S₀ to state S₂ is associated with the delay d₂, and so on. Referring again to FIG. 6A, if the downhole tool detects a first power cycle event and then, after a delay of d₁, detects a second power cycle event, the tool will transition from state S₀ to state S₁. If, as shown in the example of FIG. 6B, the downhole tool detects two power cycle events that occur with a delay of d₂, the tool will transition from state S₀ to state S₂. (It should be noted that the state diagram of FIG. 7 is intended to illustrate timing-based state transitions, and a complete state diagram would likely include additional states and/or transitions that return the system to state S₀.)

The use of timing information associated with power cycle events can also be used to communicate data to the downhole tool. For example, the tool may be placed in an operating state in which it expects to receive an operating parameter value through the use of power cycle events. Then, a series of power cycles may be performed, where each successive power cycle is delayed by an interval that corresponds to a single digit of the communicated value. The downhole tool may be configured to interpret a delay of one second as a “1”, a delay of two seconds as a “2”, and so on. The tool may be configured to interpret particular delays as decimal points, negative signs, start or end indicators, etc. If there are only a few possible values, particular delays may be assigned to those specific values when the tool is originally configured. The downhole tool could then determine a delay between power cycles, interpret this delay as an index value, and use the index value to select the desired operating parameter value from a lookup table. A lookup table could also be used to associate specific delays with corresponding operational states as shown in FIGS. 6A, 6B and 7.

As noted above, alternative embodiments may use power cycle sequencing as a means of not only mode selection, but also as a means to update various data parameters within the gauge's memory and/or communicates a formalized data packet structure. In one embodiment, a mode can be activated via a power cycle sequence to initiate the interpretation of following power cycle events as pieces of a data stream. Data compression methods can be implemented, for example, by determining binary states of the provided power as well as bit widths. A high binary state is associated with “power on”, and a low state is associated with the absence of power. Bit widths can, for instance, be associated with the elapsed time during the “power on” state. Both the binary state and different bit widths can be used to communicate compressed data. For example, if a series of four power cycles is implemented, and the on-states are sequentially transmitted with three on-time thresholds, then a base-4 interpretation could yield a base-2 compression ratio of 50% (4 power cycle events/8 bits). This is illustrated in Table 1 below. By varying both the number of power cycle events and the number of defined time thresholds per event, better compression ratios can be realized. The effective compression ratios for various numbers of power cycle events and timing thresholds are shown in Table 2 below. This would greatly enhance the capability of sending more complex data, as compared to a simplistic counter-based method.

TABLE 1 Number of timing thresholds 3 4 5 6 Power cycle events 2 4 5 6 7 3 6 8 10 11 4 8 10 12 14 5 9 12 14 16 6 10 13 16 18 7 11 14 17 20 8 12 15 18 21 9 13 16 19 22 10 13 17 20 23

TABLE 2 Number of timing thresholds 3 4 5 6 Power cycle events 2 50% 40% 33% 29% 3 47% 38% 32% 27% 4 50% 40% 33% 29% 5 54% 43% 36% 31% 6 58% 46% 39% 33% 7 62% 50% 42% 36% 8 67% 53% 44% 38% 9 71% 57% 47% 41% 10 75% 60% 50% 43%

In order to implement timing-based interpretation of the power cycle events, it will be necessary to provide a clock or other timing mechanism within the downhole tool. The timing mechanism may provide a running counter corresponding to the interval during which the tool is powered on between power cycle events. Alternatively, a real time clock that associates timestamps with the events can be provided so that the delays can be determined from the timestamps. In one embodiment, timing of power cycle events occurs only when the downhole tool is powered on, so it is not necessary to provide a battery to power the timing mechanism. In other embodiments, a battery or other non-interruptible power source for the timing mechanism may be provided to allow the timing mechanism to remain operable when the downhole tool is powered off.

It should be noted that alternative embodiments may have a number of variations on the features described above. For instance, while the foregoing embodiments utilize power cycle events to communicate state changes and operating information to the downhole tools, other types of events (e.g., mechanical movement of the tool) may also be used to communicate this information. In regard to the non-volatile memory used in the downhole tool, a flash-type memory could be used, or other types of memory or mechanical storage devices could be used, particularly in high temperature conditions. Numerous other variations may also be apparent to those of skill in the art.

Those of skill will further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software (including firmware,) or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Those of skill in the art may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The benefits and advantages which may be provided by the present invention have been described above with regard to specific embodiments. These benefits and advantages, and any elements or limitations that may cause them to occur or to become more pronounced are not to be construed as critical, required, or essential features of any or all of the claims. As used herein, the terms “comprises,” “comprising,” or any other variations thereof, are intended to be interpreted as non-exclusively including the elements or limitations which follow those terms. Accordingly, a system, method, or other embodiment that comprises a set of elements is not limited to only those elements, and may include other elements not expressly listed or inherent to the claimed embodiment. 

1. A system comprising: control equipment positioned at the surface of a well; a downhole tool positioned within the wellbore of the well; and a power cable coupled between the control equipment and the downhole tool; wherein the downhole tool is configured to receive power through the power cable; wherein the control equipment is configured to control the delivery of power through the power cable to the downhole tool and to thereby selectively power cycle the downhole tool; and wherein the downhole tool is configured to modify operation of the downhole tool in response to being power cycled.
 2. An apparatus comprising: a downhole tool configured to be positioned within the wellbore of a well; wherein the downhole tool is configured to modify operation of the downhole tool in response to power cycle events.
 3. The apparatus of claim 2, wherein the downhole tool includes a non-volatile memory, wherein the downhole tool is configured to store at least one operational state of the downhole tool, wherein the downhole tool is configured to modify the at least one operational state in response to the power cycle events.
 4. The apparatus of claim 3, wherein the non-volatile memory stores a plurality of operational states, wherein modifying the at least one operational state comprises operating in a first one of the plurality of operational states and then operating in a different one of the plurality of operational states.
 5. The apparatus of claim 4, wherein the downhole tool is configured to increment between the operational states in response to the power cycle events.
 6. The apparatus of claim 4, wherein a first function performed in the first one of the plurality of operational states is different from a second function performed in the different one of the plurality of operational states.
 7. The apparatus of claim 4, wherein a first function is performed in both the first and different ones of the plurality of operational states, wherein the downhole tool operates using a first set of operating parameters in the first operational state and a different set of operating parameters in the different one of the plurality of operational states.
 8. The apparatus of claim 2, wherein the downhole tool is configured to determine one or more timing associated with successive power cycle events, identify one or more modifications of the operation of the downhole tool corresponding to the delays, and implement the one or more modifications in the operation of the downhole tool.
 9. The apparatus of claim 8, wherein the one or more modifications comprise a state change.
 10. The apparatus of claim 8, wherein the one or more modifications comprise changing one or more operating parameters of the downhole tool.
 11. The apparatus of claim 10, wherein the downhole tool is configured to selectively enter a state in which a number and power-on durations of subsequent power cycles are determined and interpreted as compressed data values.
 12. The apparatus of claim 2, wherein the downhole tool comprises a downhole gauge which is configured to sense one or more conditions downhole and to transmit data corresponding to the downhole conditions to equipment positioned at the surface of the well.
 13. A method implemented in a downhole tool, the method comprising: powering up a downhole tool and thereby causing the downhole tool to operate in a first operational state of the downhole tool; and power cycling the downhole tool and thereby causing the downhole tool to operate in a second operational state which is different from the first operational state.
 14. The method of claim 13, wherein the downhole tool incorporates a non-volatile memory that stores a plurality of operational states including the first and second operational states.
 15. The method of claim 14, wherein the downhole tool increments between the plurality of operational states in response to detecting power cycle events.
 16. The method of claim 14, wherein in the first operational state, the downhole tool performs a first function, and in the second operational state, the downhole tool performs a second function which is different from the first function.
 17. The method of claim 14, wherein in both the first and second operational states, the downhole tool performs a first function, wherein in the first operational state, the downhole tool performs the first function using a first set of operating parameters, and in the second operational state, the downhole tool performs the first function using a second set of operating parameters which is different from the first set of operating parameters.
 18. The method of claim 13, further comprising determining one or more delays between successive power cycle events, identifying one or more modifications of the operation of the downhole tool corresponding to the delays, and implementing the one or more modifications in the second operational state.
 19. The method of claim 18, wherein the one or more modifications comprise changing the function of the downhole tool.
 20. The method of claim 18, wherein the one or more modifications comprise changing one or more operating parameters of the downhole tool.
 21. The method of claim 20, further comprising selectively placing the downhole tool in a state in which a number and power-on durations of subsequent power cycles are determined and interpreted as compressed data values.
 22. The method of claim 13, wherein the downhole tool comprises a downhole gauge, and wherein operate in at least one of the first and second operational states comprises sensing one or more conditions downhole and transmitting data corresponding to the downhole conditions to equipment positioned at the surface of a well. 